Re: Q: BLV for function slots + BL obarray/hmap for symbol lookup?

[Stefan Monnier]

Arthur Miller [2021-05-30 04:30:24] wrote:
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>>>>     (setq-local obarray (obarray-copy obarray))
>> [...]
>>> (setq-local obarray (copy-sequence obarray))
>>
>> obarray-copy != copy-sequence
> My Emacs 27.1 says void function obarray-copy,

Indeed, it's not provided.

> but copy-sequence worked.

Not really, no.  You just haven't noticed the breakage yet.

>  Aren't obarray just vectors?

No, they're very special vectors.  E.g.:

    (let ((oa (make-vector 1 nil)))
      (intern "foo" oa)
      (intern "bar" oa)
      (intern "baz" oa)
      oa)

    ==>

      [baz]

Yet, `foo` and `bar` are definitely still in there.

> For your previous mail; yes I am quite aware this is very use-case
> specific solution. Anything done elsewhere, outside that particular
> buffer after the copy is performed will not be visible in that buffer,
> as well as no definition will escape to rest of the Emacs, so this
> buffer can only be used to change state of this particular buffer and
> nothing else, and that can be quite brittle. For the bad and good. I
> haven't experimented enough yet, just a bit, I am not sure how it will
> work with Emacs state internally, gc? etc.

AFAIK I think it can be made to work, yes.
I don't expect any problem from "Emacs state internally" or the GC.

The only source of trouble I can foresee is if "normal code" ends up
running while your obarray is the one held in the global `obarray` var.
This is because "normal code" will occasionally load files (via
`require` or autoloads, typically) and that can quickly lead to
confusion.


        Stefan